1. Field of the Invention
The present invention relates in general to a cleaning method, in particular, the present invention relates to a post-cleaning method of a via etching process.
2. Description of the Related Art
In the semiconductor processing for pursuing the goal of minute line width and high integration, the product yield is greatly concerned with particles. In particular, during a via etching process, the residues remaining in the via will cause the electrical-connecting property between metal layers to deteriorate.
Please refer to FIG. 1 and FIG. 2. FIG. 1 is a cross-sectional schematic diagram of a via according to the prior art. FIG. 2 is a flow chart of a post-cleaning method of a via etching process according to the prior art. A wafer 10 comprises a substrate 12, a metal layer 14 formed on the substrate 12, an oxide layer 16 covered on the metal layer 14, and a photoresist layer 18 coated on the oxide layer 16. By using a dry etching process, a via 20 is patterned to pass through the photoresist layer 18 and the oxide layer 16 till exposing a predetermined area of the metal layer 14. In a post-cleaning method of the via etching process, the step 22 of a photoresist strip process is firstly performed to remove the photoresist layer 18 by a dry etching process in a plasma reactor, wherein the hydrocarbon inside the photoresist layer 18 is reacted with oxygen plasma to be stripped off and the produced gas, such as CO, CO2 and H2O is pumped by a vacuum system. However, the photoresist strip process also produces polymer residues and which mostly remain in the via 20. For this reason, the step 24 of a wet cleaning process is performed for cleaning off the polymer residues. In general, the wafer 10 is dipped into a sink filled with a specific etching solution, such as ACT, EKC or other alkaline compounds, on an appropriate condition of dipping time, temperature and solution concentration so as to make the polymer residues react with the etching solution to be removed off. Finally, at the step 26 of a water-rinsing process, the wafer 10 is turned vertically to ensure the fringe of the wafer 10 being cleaned off, and then the wafer 10 is dipped into deionized water to clean off the remaining etching solution.
Nevertheless, the wet cleaning method that utilizes the chemicals such as ACT and EKC with high waste volume encounters problems such as increasing cost of the chemicals and a shortage of chemical resources. It does not conform to expectations for the cost considerations of mass production. Also, since dipping the wafer 10 into the etching solution consumes a period time to make the polymer residues completely react with the etching solution, the overall via etching process period is increased.
Therefore, the present invention provides a post-cleaning method of a via etching process, which substitutes a dry cleaning process for the wet cleaning process to solve the above-mentioned problems.
A post-cleaning method of a via etching process for cleaning a wafer, the wafer comprising a tungsten (W) layer, an oxide layer covered on the tungsten layer, a photoresist layer patterned on the oxide layer, and a via passing through the photoresist layer and the oxide layer till exposing a predetermined area of the tungsten layer, the cleaning method comprises the steps of: (a) performing a photoresist strip process to remove the photoresist layer; (b) performing a dry cleaning process which uses CF4 and N2H2 as the main reactive gas; and (c) performing a water-rinsing process.
It is an advantage of the present invention that since the dry cleaning process substitutes the wet cleaning process to remove the polymer residues without using costly and rare alkaline compounds, the production cost is substantially decreased. Also, the dry cleaning process can quickly remove the polymer residues and the wafer needs not to be turned vertically before dipping into deionized water, so the overall post-clean process becomes more efficient. Furthermore, the photoresist strip process and the dry cleaning process can be performed in-situ; therefore this will facilitate the post-clean process.
This and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiment, which is illustrated in the various figures and drawings.